There are various types of drive tools like a nail driver and a rivet driver which drive a nail, a pin, a rivet and others into a workpiece material. The drive tools can be classified mainly into air type drive tools which utilize compressed air as the drive source and gas combustion type drive tools which utilize gas combustion pressure as the drive source.
Specifically, in gas combustion type drive tools, unlike air type drive tools, it is not necessary to provide an air source separate from the tool body and an air hose for connecting therebetween. A gas can filled with fuel gas is loaded to the tool body. With the fuel gas from the gas can, a drive source for driving in is generated on the same principle as internal-combustion engine of an automobile (see Patent Document 1, for example).
More particularly, a gas combustion type drive tool includes a cylinder and a piston inside the tool for transmitting to such as a nail a pressure upon gas combustion as a drive power for driving in. Upon driving in, a movable portion (contact arm) at the tool end is at first pressed against a workpiece material (a driven object) to slide the contact arm to the back side of the tool body. Thereby, inside the tool body, a certain amount of fuel gas is supplied from a gas can into a sealed combustion chamber provided in an upper portion of the cylinder. At the same time, a fan provided inside the combustion chamber rotates to mix/stir air and fuel gas inside the combustion chamber.
When a trigger is pulled this state, an igniter provided to face the interior of the combustion chamber sparks to explode the fuel gas inside the combustion chamber. Due to the pressure upon the explosion, the piston is linearly driven to the tool end side. On the tool end side in the piston, a bar-like driver blade for ejecting such as the nail to the workpiece material side is provided in a fixed manner. When the piston is rapidly moved toward the tool end side due to the explosion of the fuel gas, the driver blade as well is rapidly moved toward the tool end side at the same time. Due to the rapid move of the driver blade, such as the nail is pressed/ejected to the workpiece material side and driven into the workpiece material.
As noted above, in a gas combustion type drive tool, a series of driving operation can be done only with the tool body loaded with a gas can. As compared to an air type drive tool, the gas combustion type drive tool has the advantage of being superior in mobility and workability.
Also in the above-described gas combustion type drive tool, a mechanism is generally installed which disables driving of such as a nail unless the trigger is pulled under the condition that the contact arm provided at the tool end is pressed against the workpiece material. A typical example of such mechanism is a structure (mechanism) in which the trigger is unable to be pulled unless the contact arm is pressed against the workpiece material and slid to the back side of the tool body. More particularly, in order to drive in such as a nail, the contact arm has to be pressed against the workpiece material before the trigger is pulled. Such mechanism is adopted (installed) in most gas combustion type drive tools.    Patent Document 1: Unexamined Japanese Patent Publication No. 2005-199397